It has long been recognized that the properties of polymers can be tailored to a high degree through variables such as polymer sequence, structure, additive and filler incorporation, composition, morphology, thermodynamic and kinetic processing control. It is similarly known that various sizes and shapes of fillers, and particulates (e.g. calcium carbonate, silica, carbon black etc.) can be incorporated into preformed polymers or prepolymers or monomer mixtures to enhance physical and material properties of the resulting formulations.
In their solid state all polymers (including amorphous, semi-crystalline, crystalline, and rubber, etc.) possess considerable amounts of internal and external free volume (see FIG. 1). The free volume of a polymer has a tremendous impact on its physical properties, since it is within this volume that the dynamic properties (e.g. reptation, translation, rotation, crystallization) of polymer chains primarily operate and in turn influence fundamental physical properties such as density, thermal conductivity, glass transition, melt transition, modulus, relaxation, and stress transfer.
The accessibility of free volume in a polymer system depends greatly on its morphology and on the size of the agent desired to occupy the free volume. As shown in FIG. 2, for example, denser regions and phase separation within a polymer can both increase and decrease the thermodynamic and kinetic access to such areas. Because of its influence on thermodynamic and kinetic properties, polymer morphology and free volume dimension are major factors that limit the ability of conventional fillers from accessing the free volume regions in a polymer system. Additional processing/compounding effort is normally required to force compatibilization between a filler and a polymer system because conventional fillers are physically larger than most polymer dimensions, are chemically dissimilar, and usually are high melting solids.
Prior art in fluoropolymers has focused on modifications through the formation of an inorganic interpenetrating network that is either partially or fully condensed and is in contact with or dispersed amoungst the fluoropolymer chains. See U.S. Pat. Nos. 5,876,686 and 5,726,247. Similarily modifications have been described that enhance properties through the continuous or discontinuous dispersion of macro, micro and nanoscale particulates of a dissimilar composition (e.g. inorganic) relative to that of the fluoropolymer. In either case the function of the inorganic network or filler particle is to reduce the relative slippage or motion of the fluoropolymer chains and segments relative to each other. The combination of reduced chain motion with the thermally stable inorganic component utlimately enhances physical properties such as dimensional stability, impact resistance, tensile and compressive strengths, thermal stability, electrical properties, abrasion and chemical resistance, shrinkage and expansion reduction. Unfortunately, all of the prior art either suffers from process complexity, a length scale of the reinforcement that is too large to sufficiently access polymer free volume, or reinforcement that lacks sufficient geometrical definition to provide structure regularity and reinforcement at the molecular (10−10 m) and nanoscopic (10−9 m) length scales. As illustrated in FIG. 4, fillers are geometrically ill defined solid particulates that macroscopically or nanoscopically reinforce large associated or nearby groups of polymers rather than the individual chains and segments within these polymers. As illustrated in FIG. 5, incompletely condensed or completely condensed interpenetrating networks also lack sufficient geometrical definition to provide structure regularity and reinforcement of fluoropolymer chains.
Furthermore, it has been calculated that as filler sizes decrease below 50 nm, they would become more resistant to sedimentation and more effective at providing reinforcement to polymer systems. The full application of this theoretical knowledge, however, has been thwarted by the lack of a practical source of particulate reinforcement or reinforcements which are geometrically well defined, and monodisperse and with diameters below the 10 nm range and especially within the 1 nm to 5 nm range. Particularly desirable are monodisperse, nanoscopically sized chemicals with precise chemical compositions, rigid and well defined geometrical shapes, and which are dimensionally large enough to provide reinforcement of polymer chains. Such nanoscopic chemicals are desirable as they are expected to form the most stable dispersions within polymer systems, would be well below the length scale necessary to scatter light and hence are visually nondetectable when incorporated into fluoropolymers, and would be chemically compatible with fluoropolymers and dissolve into and among the polymer chains, thus eliminating the need for extensive dispersion or reactive self assembly or the complex processing requirements of the prior art.
Recent developments in nanoscience have enabled the ability to cost effectively manufacture commercial quantities of materials that are best described as nanostructured chemicals due to their specific and precise chemical formula, hybrid (inorganic-organic) chemical composition, large physical size relative to the size of traditional chemical molecules (0.3–0.5 nm), and small physical size relative to larger sized traditional fillers (>50 nm).
Nanostructured chemicals are best exemplified by those based on low-cost Polyhedral Oligomeric Silsesquioxanes (POSS) and Polyhedral Oligomeric Silicates (POS). FIG. 3 illustrates some representative examples of monodisperse nanostructured chemicals, which are also known as POSS Molecular Silicas.
These systems contain hybrid (i.e., organic-inorganic) compositions in which the internal frameworks are primarily comprised of inorganic silicon-oxygen bonds. The exterior of a nanostructure is covered by both reactive and nonreactive organic functionalities (R), which ensure compatibility and tailorability of the nanostructure with organic polymers. These and other properties of nanostructured chemicals are discussed in detail in U.S. Pat. Nos. 5,412,053 and 5,484,867, both are expressly incorporated herein by reference in their entirety. These nanostructured chemicals are of low density, exhibit excellent inherent fire retardancy, and can range in diameter from 0.5 nm to 5.0 nm.
Prior art associated with fillers, plasticizers, interpenetrating networks, and polymer morphology has not been able to adequately control polymer chain, coil and segmental motion at the 1 nm–10 nm level. Furthermore, the mismatch of chemical potential (e.g., solubility, miscibility, etc.) between fluoro-based polymers and inorganic-based fillers and chemicals results in a high level of heterogeneity in compounded polymers that is akin to oil mixed with water. Therefore, there exists a need for appropriately sized chemical reinforcements for polymer systems with controlled diameters (nanodimensions), distributions and with tailorable chemical functionality. In addition, it would be desirable to have easily compoundable nanoreinforcements that have chemical potential ranges (misibilities) similar to the various fluorinated polymer and fluorinated fluid systems.